Oxygen injection through a roof or crown of a glass furnace

ABSTRACT

A method is provided to facilitate combustion in a furnace having at least one burner, an inlet, an outlet, and sidewalls and a crown defining a combustion chamber for the furnace, the method consisting of identifying a region of the combustion chamber where a furnace atmosphere therein requires an increase in oxygen for combustion in the furnace atmosphere, and providing fresh oxygen to the region at a controlled flow rate for the combustion, wherein the fresh oxygen provided causes circulation of the furnace atmosphere for combining existing gases and existing oxygen of the furnace atmosphere with the fresh oxygen provided to the region for combustion.

BACKGROUND OF THE INVENTION

The invention relates to injection of oxygen in furnaces.

Furnaces, such as glass melting furnaces, which require additionaltonnage/quality or are operating at reduced tonnage due to damage ordegradation of heat recovery devices in the form or regenerators orrecuperators, have used oxygen and oxygen burners, and fuel burners togain additional tonnage/quality or recover lost production.

Oxygen enrichment is typically achieved by introducing oxygen into thecombustion air downstream of the forced combustion air fan or blower forthe furnace. The required equipment is minimal and therefore is a lowcost installation. The oxygen is injected at a location that ensures theoxygen is well blended with the combustion air. Injecting pure 100%oxygen into an air stream means that approximately five times the volumeof air can be removed to provide the same amount of oxygen. The actualpercentage of oxygen that is possible is determined by local/CGA(Compressed Gas Association) codes and HAZOPs (Hazardous OperationProcedures), but is always less than 29% on a volumetric basis and moretypically less than 25%. It should be noted that with respect toenrichment, the point of combustion is indiscriminate. For example, if afirst port of a four port cross-fired regenerative furnace is partiallyblocked, the location at which the oxygen is really required is in thefirst port area. Since the remaining ports offer a path of lowerresistance, there is proportionally more oxygen that goes where it isnot required/desired. General enrichment may be the least expensive asfar as cost of installation, but it is the least efficient method ofusing oxygen where it is needed in furnaces.

Oxygen lancing overcomes many of the disadvantages of enrichment byinjecting oxygen at the location where it is needed most. Lancing isaccomplished by underport, through-port, over-port, side-of-port or fromthe regenerator target wall. For example, if the first port of a fourport cross-fired regenerative furnace is partially blocked, the locationat which the oxygen is required is in the first port area and therefore,it is in this area that the majority of the oxygen is injected. Aregenerative furnace has a reversal system and therefore, it isnecessary in such a furnace to have a relatively complex and expensivecontrol system to feed a correct amount of oxygen to the correct port.Typically, if a lancing system is installed with the furnace it willfeed oxygen to at least a plurality of ports. Since the oxygenrequirements may vary from one side to the other, there is a requirementfor flow control on each side of the furnace. A reversing three-portlancing panel would therefore require six zones of control. There isalso a limit to the amount of oxygen that can be injected in the portarea. Higher levels of oxygen in the port can cause too much heatrelease in the port area, thereby causing structural damage. Inunder-port applications, the flames can become too short and create animbalance in heat distribution which can cause glass defects.

Oxygen enrichment and lancing have been used to recover up to 10% oflost furnace melt capacity.

When additional capacity is required, there is typically a need for fuelflows beyond the capacity of the installed air fuel system for thefurnace. Oxy-fuel boosting involves the placement of at least one andsometimes a plurality of oxy-fuel burners in the zero port (area betweencharging wall and the first port) or in the hot spot (point of upwellmelt area in furnace) of the furnace. Conventional oxy-fuel burners caneither recover lost production from a furnace or increase capacity by atleast 10%, and occasionally as high as 15%. The furnace design usuallydetermines the capacity that can be obtained and where, if possible,burners can be positioned and installed. Installation is costly, since adedicated oxygen and fuel control skid is typically required. Theoverall system capacity is determined by the exhaust capacity of thefurnace.

When there are space constraints in the furnace, or capacity in excessof 15% is required, it is possible to install oxy-fuel burners in thecrown or roof of the furnace. A significant amount of energy can beinjected into the furnace using roof mounted burners. It is possible toblock-off existing air-fuel ports and replace the air-fuel ports withoxy-fuel. In extreme cases it is possible to create a 100% oxy-fuelfurnace or in a transition phase for the furnace convert to a hybridfurnace with oxy-fuel for melting and air fuel forrefining/conditioning.

One of the major disadvantages of oxy-fuel boosting, especially whenused with cross-fired regenerative furnaces, is the turndown (reductionin firing capacity) of the burners. This is common to both conventionalor crown mounted burners. In order to avoid flame distortion orinteraction, there is a minimum flowrate that is required. At certaintimes due to production or product mix, it is necessary to use moreoxygen than is really required.

Mathematical modeling shows that when converting a zero portconventional oxy-fuel boost to roof mounted burners firing with the sameamount of oxygen and fuel, there has been a change in distribution ofthe excess oxygen in the exhaust ports. While providing fuel and oxygenthrough a burner in the crown provides more oxygen in the first andsecond ports than with conventional horizontal style burners, there isstill the deficiency in known systems of not having enough oxygen tocombust as necessary in certain areas of the furnace and for particularmelt operations.

Since air is 20.9% oxygen, with the balance being nitrogen and noblegases, replacing air with oxygen provides a reduction in volume of79.1%. If furnace pressure is a limitation on combustion and flowrate,then replacing air with oxygen, even partially, can solve the problem asdiscussed below.

SUMMARY OF THE INVENTION

There is provided injection of oxygen through a crown of a furnace, suchas a glass furnace, into a selected region of the furnace to enhance thefurnace atmosphere convection flow patterns, thereby providing furnacegases with higher concentrations of oxygen. There is provided moreefficient combustion in a furnace to recover or provide additionalcapacity by positioning the oxygen at the point of greatest combustionneed; and flexibility to safely inject oxygen into and at increasedamounts to specific areas or zones of the furnace.

There is also provided a system, whereby at least one or a plurality ofoxygen jets or oxygen injectors are disposed in the roof or crown of thefurnace at select positions with respect to the ports of the furnace forinjecting oxygen into the combustion atmosphere of the furnace tofacilitate a venturi effect of said atmosphere and induce entrainedoxygen in the existing furnace atmosphere to areas desired forcombustion.

The system of the present invention also reduces NOX (nitrous oxides).

The oxygen (O₂) injection and selected flow of oxygen increases thetemperature of the furnace and facilitates combustion in the furnace.This is useful for existing furnaces where there is insufficient spacefor installing additional burners.

There is provided by the present invention a selected region identifiedin the furnace where the oxygen is needed and therefore injected intothe furnace atmosphere near an inlet of the furnace and before a firstport or burner of the furnace; the first port being the port closest tothe inlet of the furnace. Injection of the O₂ may be in registrationwith, but not be limited to, the longitudinal centerline of the furnace.

A method is provided to facilitate combustion in a furnace having atleast one burner, an inlet, an outlet, and sidewalls and a crowndefining a combustion chamber for the furnace, the method consisting ofidentifying a region of the combustion chamber where a furnaceatmosphere therein requires an increase in oxygen for combustion in thefurnace atmosphere, and providing fresh oxygen to the region at acontrolled flow rate for the combustion, wherein the fresh oxygenprovided causes circulation of the furnace atmosphere for combiningexisting gases and existing oxygen of the furnace atmosphere with thefresh oxygen provided to the region for combustion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal cross-section of a cross-fired regenerativefurnace having an oxygen injector of the invention for facilitating gasflow along an interior of the furnace proximate the crown and towardcombustion zones of the furnace.

FIG. 2 shows a lateral cross-section of the furnace of FIG. 1, having aplurality of the oxygen injectors across the furnace width.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, there is shown a furnace 10, such as a glassmelting furnace, which includes a roof or crown 12. A regenerator 14 orplurality of regenerators are disposed for communication and operationaluse with the furnace 10. The regenerators 14 are in communication with afurnace atmosphere “A” of the furnace 10. The regenerators 14 eachinclude checkers 15. A batch charging system 16 is in communication withthe furnace 10 at an inlet 18 of the furnace for providing batch 20, asin this case glass seed, to the furnace for the melt. A glass bath isshown generally at 22. Exhaust flow from the furnace 10 is showngenerally at 24, moving from the furnace 10 combustion atmosphere A tothe regenerator 14.

One or a plurality of ports 26 (numbered 1-7) are disposed along opposedsides of the furnace 10. One or a plurality of oxygen injectors 28 aredisposed in the crown 12 of the furnace 10. Each one of the oxygeninjectors 28 may be formed as a tube constructed from, for example,metal or ceramics. The oxygen injector 28 may be positioned anywherealong the crown 12 of the furnace 10. That is, each oxygen injector 28can be positioned to be in registration with a corresponding one of theports 26 or arranged to be positioned between the ports 26. In addition,an oxygen injector 28 can be positioned as shown in FIG. 1, i.e. betweenthe inlet 18 or the batch charging system 16 and the port 26 (#1) of thefurnace 10. Similarly, the oxygen injector 28 can be positionedproximate to an outlet 30 (glass discharge section or throat) of thefurnace 10, at any location along the crown 12 such as also at alongitudinal centerline “C” of the furnace 10.

The oxygen injector 28 may comprise a pipe or tube having the necessarysealing member or component where the pipe is introduced through thecrown 12 of the furnace 10. One end of the oxygen injector 28 isconnected to an oxygen source (not shown) while an opposed end of theinjector 28 terminates in the furnace atmosphere A as shown in FIGS. 1and 2. Each injector 28 has its own controllable flow rate to provideits respective oxygen profile 29. A plurality of injectors 28 may havetheir flow rates adjusted to provide a combined oxygen and burn profileselected for the particular glass bath 22 or melt.

The oxygen injectors 28 may be disposed in the crown 12 of the furnace10 at a position whereby the oxygen jet is introduced into the furnacevertically (at 90° to the bath 22) and up to an angle 32 as much as 45°with respect to the vertical as shown in FIG. 1. Some furnaces have athroat which is located at an outlet of the furnace below the glassline. The oxygen injectors 28 may be used with existing burners beingused in the furnace 10.

Injection of a gaseous oxygen stream through the crown 12 of the furnace10 generates a venturi (suction) effect in the furnace to draw gasesfrom other parts of the furnace in the form of a circulatory currenttoward the injected stream for combustion. Such a circulatory currentflow is shown generally by arrow 34. Depending on the point of oxygeninjection, such will determine what gases are drawn into the oxygenstream. For example, in most cross-fired furnaces there is more oxygenin the downstream ports 26 (such as port #s 5-7) than the upstream ports26 (port #s 1-4). However, it is desirable to have a sufficient amountof oxygen in the upstream ports 26. Therefore, injecting a gaseousstream in the upstream zone of the furnace draws furnace gas of higheroxygen concentration from the downstream ports 26 (port #s 5-7) towardthe upstream ports 26 (for example, port #s 1-4).

In the invention, the injected gaseous stream contains oxygen from 20.9%to 100%. However, due to the entrainment of additional oxygen moleculesfrom an area in the furnace 10 with higher localized oxygenconcentration, the total oxygen conveyed to the flame as a result of theventuri effect can be greater than the amount of oxygen injected by theinjectors 28, with the combustion air supply shown generally at 36. Thisis the total of oxygen injected with the oxygen injectors 28 plus theentrained oxygen stream. The entrained stream will comprise compounds ofoxygen, nitrogen, carbon monoxide, carbon dioxide, water, noble gases,gases of evolution from the glass, and combinations thereof.

As shown in FIG. 2, having a plurality of gaseous injectors 28 disposedacross the crown 12 results in a port fire flame for the furnace beingprovided with the additional oxygen introduced from the oxygen injector28 and the flow stream 34 as it crosses the surface of the glass melt22. This flame injection of furnace gases will reduce overall nitrousoxide (NOx) formation by the increased efficient combustion.

The gaseous oxidant stream flow 34 facilitated by the venturi effect ofthe injected oxygen resembling the circulatory current will contact theglass batch surface 38 and provide a localized high concentration ofoxygen under the flame created by the combustion air supply 36 andburner being used in the furnace 10. This flow 34 will combust the flameand ensure complete combustion prior to exiting through exhaust 24 ofthe furnace 10. The resulting flame temperature in the furnace 10 willbe increased and in turn will increase the localized heat transfer tothe glass bath 22.

Utilizing a portable gas analyzer during commissioning and processoptimization of the furnace 10 will enable the desired furnace fuelprofile and heat release to be achieved with the minimum amount ofoxygen to be injected and used.

An important aspect of this invention is to recover unused oxygen in thefurnace atmosphere and to reduce NOX (nitrous oxide) of the furnace. Todo this, the oxygen stream may be directed down from the lateralcenterline of the furnace 10 at an angle so as to sweep under the port26 (#1). To reduce NOX, the amount of oxygen injected under combustionfire will stoichiometrically complete the combustion of the fuel orexceed the stoichiometric amount of oxygen to complete the combustion ofthe fuel. Injecting the oxygen toward or at the centerline C of thefurnace has the benefits of not overheating the wall of the furnacethrough which the incoming fuel is passing and avoiding wasting theoxygen by combusting the oxygen with the fuel-gas over the batch ratherthan at or in the exhaust flow 24 or in the regenerator 14. When thestream of oxygen passes under the path of the fuel-gas, it will pull thefuel-gas down over the batch as it is combusted and reduce the amount ofenergy that will heat the superstructure of the furnace or theregenerators. This equates to a more efficient process of transferringenergy into the bath 22 and accelerating the melting of the batch.

The oxygen injector 28 does not have to provide 100% oxygen. Forexample, oxygen content injected could be in a range of 70% oxygen and30% gas. There are advantages to operating the injector 28 with somefuel rather than being 100% oxygen. One advantage is that it wouldprovide thrust to the injected oxygen stream to ensure same will passunder the first port 26 fires. This thrust would be affected bydifferent variables in the furnace operation, such as for example thedistance of the crown to the bath 22, the speed of the circulatory flow34 across the furnace, the amount of the gas in the first port.

In order to have a port firing on the reducing side of stoichiometry,one has to either partially or completely block off that port to limitthe amount of combustion air that would pass through that port or addadditional fuel through that port that exceeds the stoichiometric amountof oxygen that would be in the combustion air passing through this port.In this case, the amount of air that passes though a port isproportioned by the area of that port relative to the total area of allthe incoming ports. This occurs in the regenerator 14 in which all theincoming combustion air passes through a common manifold above thecheckers 15 before entering the ports.

The oxygen injectors 28 can be used on the furnace 10 regardless ofwhether the furnace is providing float, container, lighting, display orspecialty glass.

It will be understood that the embodiments described herein are merelyexemplary, and that a person skilled in the art may make many variationsand modifications without departing from the spirit and scope of theinvention. All such variations and modifications are intended to beincluded within the scope of the invention as described and claimedherein. It should be understood that embodiments described above are notonly in the alternative, but may also be combined.

1. A method to facilitate combustion in a glass melting furnace havingat least one burner, an inlet, an outlet, sidewalls and a crown defininga combustion chamber for the furnace, the method comprising: identifyinga region of the combustion chamber where an atmosphere of the furnacerequires an increase in oxygen for combustion in the furnace atmosphere;injecting fresh oxygen through an injector in the crown of the furnaceto the region at a controlled flow rate for the combustion; generating asuction effect for the furnace atmosphere in the combustion chamberresponsive to the fresh oxygen provided, wherein the furnace atmospherecirculates for combining existing gases and existing oxygen in thefurnace atmosphere with the fresh oxygen provided to the region forcombustion.
 2. (canceled)
 3. The method according to claim 1, whereinthe fresh oxygen injected is in a gaseous stream containing from 20.9%to 100% oxygen.
 4. The method according to claim 1, wherein the injectorcomprises at least one injection port disposed at the crown of thefurnace.
 5. The method according to claim 4, wherein the at least oneinjection port comprises a tubular member having a first end connectedto a source for the fresh oxygen, and a second end terminating in thefurnace atmosphere for providing the fresh oxygen to the region forcombustion with the existing gases and the existing oxygen.
 6. Themethod according to claim 1, wherein the fresh oxygen is provided nearthe inlet of the furnace proximate the at least one burner.
 7. Themethod according to claim 1, wherein the fresh oxygen is provided to theregion in registration with a longitudinal centerline of the furnace. 8.The method according to claim 1, further comprising introducing a fluidwith the fresh oxygen to increase a delivery rate of the fresh oxygeninto the furnace atmosphere.
 9. The method according to claim 8, whereinthe fluid is selected from a combustible gas, combustible liquid andcombinations thereof.